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| United States Patent |
6,007,332
|
|
O'Brien
|
December 28, 1999
|
Tooth color matching system
Abstract
A method and system for determining the color characteristic of a tooth,
particularly in a mouth in which restorative dentistry is contemplated,
employs the photographic imaging of the tooth of the patient, and the
photographing of visually selected color standards, to achieve the final
selection of the closest color match. The resulting photographic images,
which may be on a single photograph, are subjected to calorimetric or
spectrophotometric analysis to achieve the final selection of the closest
match. The system avoids the need to rely upon the visual color acuity of
the practitioner in order to achieve a close color match for a prosthetic
device. Additionally, the method and system of the invention avoid the
problems associated with color shifts associated with photography, when
such is used alone as the indicator of tooth color.
| Inventors:
|
O'Brien; William J. (1320 Morningside, Ann Arbor, MI 48103)
|
| Appl. No.:
|
721266 |
| Filed:
|
September 26, 1996 |
| Current U.S. Class: |
433/26; 356/404; 433/203.1 |
| Intern'l Class: |
A61C 019/10 |
| Field of Search: |
433/26,29,203.1,215
365/413.28
356/402,405,406,408,404
|
References Cited
U.S. Patent Documents
| 3436157 | Apr., 1969 | Adler et al. | 356/192.
|
| 3507042 | Apr., 1970 | Hana.
| |
| 3778541 | Dec., 1973 | Bowker | 178/5.
|
| 3878384 | Apr., 1975 | Bowker | 235/151.
|
| 3986777 | Oct., 1976 | Roll | 356/176.
|
| 4608015 | Aug., 1986 | Smigel | 433/26.
|
| 4654794 | Mar., 1987 | O'Brien | 364/413.
|
| 4813000 | Mar., 1989 | Wyman et al. | 364/526.
|
| 4836674 | Jun., 1989 | Lequime et al. | 433/26.
|
| 5055040 | Oct., 1991 | Clar | 433/26.
|
| 5177694 | Jan., 1993 | Graham et al. | 364/526.
|
| 5240414 | Aug., 1993 | Thompson | 433/26.
|
| 5309257 | May., 1994 | Bonino et al. | 358/504.
|
| 5313291 | May., 1994 | Appel et al. | 358/501.
|
| 5317425 | May., 1994 | Spence et al. | 358/504.
|
| 5383020 | Jan., 1995 | Vieellefosse | 356/405.
|
| Foreign Patent Documents |
| 4301530 | Oct., 1992 | JP | 356/402.
|
| 4338465 | Nov., 1992 | JP | 433/203.
|
| 1750676 | Jul., 1992 | SU | 433/26.
|
| 8603292 | Jun., 1986 | WO | 433/203.
|
| 9002929 | Mar., 1990 | WO | 433/203.
|
| 9102955 | Mar., 1991 | WO | 433/203.
|
Primary Examiner: O'Connor; Cary E.
Attorney, Agent or Firm: Rohm & Monsanto, P.L.C.
Claims
What is claimed is:
1. A method of selecting a color standard color characteristic for a tooth
prosthesis of a patient that matches closely the color characteristic of a
selected original tooth, the method comprising the steps of:
selecting a plurality of color standards, each having a predetermined color
characteristic that is determined visually to approximate the
corresponding color characteristic of the original tooth;
photographing the original tooth and the plurality of color standards
selected in said step of selecting;
tooth color measuring the predetermined color parameter of the original
tooth from a photograph produced in said step of photographing to produce
a tooth color parameter value;
standards color measuring the predetermined color parameter of each of at
least two of the color standards from a photograph produced in said step
of photographing to produce respective standards color parameter values;
and
calculating respective values corresponding to the differences between the
tooth color parameter value and the respective standards color parameter
values, whereby the color standard associated with the smaller difference
represents the closer color characteristic match to the color
characteristic of the original tooth.
2. The method of claim 1, wherein, in said step of photographing, there are
produced a plurality of photographs representing respective color
characteristics of the tooth and the color standards selected in said step
of selecting.
3. The method of claim 1, wherein said photograph is a color print.
4. The method of claim 1, wherein said photograph is a transparency.
5. The method of claim 1, wherein said photograph is a monochrome print.
6. A method of matching the color characteristic of a tooth with a
plurality of color standards, the method comprising the steps of:
inspecting visually the tooth and the plurality of the color standards;
selecting from the plurality of the color standards a number of the color
standards that are determined in said step of inspecting visually to
approximate the color characteristic of the tooth;
photographing the tooth and the number of the color standards selected in
said step of inspecting visually;
employing a selectable one of a colorimeter and a spectrophotometer to
measure a color parameter of the images obtained in said step of
photographing of the tooth and of the selected color standards; and
determining the one of the selected color standards that is associated with
the photographic image of the selected color standards having the minimum
color difference from the tooth as determined by the measurement of said
step of employing.
7. The method of claim 7, wherein a photograph produced in said step of
photographing is a color print.
8. The method of claim 7, wherein a photograph produced in said step of
photographing is a monochrome print.
9. The method of claim 7, wherein a photograph produced in said step of
photographing is a transparency.
10. A system for determining a color characteristic of a tooth, the system
comprising:
a plurality of color standard means, each for establishing a predetermined
respective color parameter;
photographic means for producing a photographic tooth image of the tooth
and respective photographic color standard images of selected ones of said
plurality of color standard means;
means for measuring a predetermined color parameter of said photographic
tooth image to produce a tooth image signal responsive thereto and for
measuring a corresponding predetermined color parameter of each of said
photographic color standard images of said selected ones of said plurality
of color standard means to produce respective color standard image signals
corresponding to respectively associated ones of said selected ones of
said plurality of color standard means; and
means for comparing said tooth image signal to each of said color standard
image signals.
11. The system of claim 10, wherein said means for measuring comprises a
colorimeter.
12. The system of claim 10, wherein said means for measuring comprises a
spectrophotometer.
13. The system of claim 10, wherein said photographic means comprises a
camera.
14. The system of claim 13, wherein said photographic means further
comprises a color film for said camera.
15. The system of claim 13, wherein said photographic means further
comprises a monochromatic film for said camera.
16. The system of claim 13, wherein said photographic means further
comprises a transparency film for said camera.
17. The system of claim 10, wherein said photographic means comprises an
instant development-type camera.
18. The system of claim 10, wherein there is further provided lighting
means for producing a predetermined light.
19. The system of claim 10, wherein said plurality of color standard means
are each provided with an aperture for facilitating viewing of the tooth
therethrough.
20. The system of claim 10, wherein said means for comparing comprises a
numerical display associated with said means for measuring.
21. A system for determining a color parameter of a tooth, the system
comprising:
a plurality of color standards, each for establishing a predetermined
respective color parameter;
photographic means for producing a photographic tooth image of the tooth
and a respective photographic color standard image of a selected one of
the color standards;
measuring means for measuring the spectra of the photographic tooth image
and at least one of the photographic color standard images; and
calculating means for calculating the color parameter of the tooth.
22. The system of claim 21, wherein said measuring means comprises a
spectrophotometer.
23. The system of claim 21, wherein said measuring means is arranged to
calculate a color shift function characteristic of said photographic
means.
24. The system of claim 23, wherein said calculating means is arranged to
determine the color parameter of the tooth in response to the color shift
function characteristic of said photographic means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to dentistry, and more particularly, to a
system of matching dental color for facilitating and improving restorative
dental procedures.
2. Description of the Related Art
The prior art provides essentially three methods for determining the colors
of teeth in dentistry. These include, visual matching against shade guide
color standards, colorimetry, and photography. Visual matching systems
that employ shade guide color standards constitute the predominant color
matching system. With this known system, a practitioner visually matches
the color of the patient's tooth that will be restored against a series of
color standards. It is a significant problem with this known method that
its success depends upon the color vision of the practitioner. In the
practice of the known method, the practitioner first selects, by visual
inspection, standard colors that exhibit, to his or her eye, a general
match to the subject's tooth. Then, a final match is performed that
requires excellent color matching ability on the part of the practitioner.
As intimated, this known method is flawed, as the quality of the resulting
restoration is largely related to the skill of the particular
practitioner, and his or her ability to detect small color differences in
the final matching from among the closest color standards. In a study by
Kuehi & Marcus (Color Res. Appl 4: 83-91, 1979), large differences in the
ability to discriminate color was shown among plural subjects, such
ability ranging from 0.5 to 6 CIE .DELTA.E units. These measurements are
determined using the known CIE L*a*b* system described, for example, in
Bilmeyer, F. W., Principles of Color Technology, 2nd ed., John Wiley,
1981.
The prior art has sought to overcome some of the problems associated with
visual color matching systems by applying colorimetry technology to the
measurement of tooth colors in the clinic. However, this effort has not
achieved success. A colorimeter was marketed in the 1970's (Chromoscan
from Stemdent, N.Y.), but the unit failed to achieve adequate color
discrimination (O'Brien & Nelsen, J. Prosthet. Dent. 49: 63-66, 1989). A
more recent effort to overcome the stated problems is described in U.S.
Pat. No. 4,654,794 ("O'Brien"), and employs a spectrophotometer. However,
the prototype results were disappointing.
There are two major technical obstacles to successful clinical
implementation of calorimeters to the measurement of tooth colors. First,
the measurement of the color of translucent objects, specifically
including teeth, suffers from inaccuracies that result from so-called
"edge effects." As light from the calorimeter enters the tooth for
measurement, it is scattered sideways away from the edges of the light
beam. This results in significant diminution in the magnitude of light
signal that is returned to the sensor. The second problem relates to the
application of the calorimeter probe to the surface of the teeth, since
teeth are irregular in shape. Colorimeters are designed to achieve
accuracy of color measurement on flat, opaque objects.
Finally, photography has been used to show the color of teeth in lectures
and textbooks, but it is known to be extremely inaccurate in reproducing
color. During the several stages of the photographic process,
uncorrectable color shifts take place which render accurate and reliable
color reproduction not to be feasible. Nevertheless, practitioners
regularly send photographs of patients' teeth to dental laboratories to
show the approximate color.
It is, therefore, an object of this invention to provide a system for
accurately determining the color of the teeth of a dental patient, without
complete color discrimination reliance on the practitioner.
It is another object of this invention to provide a method producing a
reliable record of color difference between the teeth of a dental patient
and a color standard.
It is also an object of this invention to provide a method of selecting
from a plurality of color standards, a color standard corresponding to the
closest color match to the tooth of a dental patient;
It is a further object of this invention to provide a method of selecting
from a plurality of color standards, each having a respectively associated
color parameter, a one of the color standards corresponding to the closest
color parameter match to the tooth of a dental patient;
It is additionally an object of this invention to provide a method of
selecting from a plurality of color standards, each having a respectively
associated color characteristic, a one of the color standards
corresponding to the closest color parameter match to the corresponding
color characteristic of a test subject.
It is yet a further object of this invention to provide a system for
determining the color composition of a tooth whereby a restoration
material can be formulated in response thereto.
It is also another object of this invention to provide a method of
estimating the color parameters of a tooth of a dental patient.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by this invention which
provides a method of selecting a color standard color characteristic for a
tooth prosthesis that closely matches the color characteristic of a
selected original tooth. In accordance with the invention, the method
includes the steps of:
1. selecting a plurality of color standards, each having a predetermined
color characteristic that is determined visually to approximate the
corresponding color characteristic of the original tooth;
2. photographing the original tooth and the plurality of color standards
selected in the step of selecting;
3. tooth measuring the predetermined color parameter of the original tooth
from a photograph produced in the step of photographing to produce a tooth
color parameter value;
4. standards measuring the predetermined color parameter of each of at
least two of the color standards from a photograph produced in the step of
photographing to produce respective standards color parameter values; and
5. calculating respective values corresponding to the differences between
the tooth color parameter value and the respective standards color
parameter values, whereby the color standard associated with the smaller
difference represents the closer color characteristic match to the color
characteristic of the original tooth.
In a preferred embodiment of the invention, the determination of the color
parameters of the dental patient's tooth is based upon the measured shift
in color of a standard in the same photograph by the photographic process.
The shift function of the standard in the photograph is used with an
algorithm to calculate the original color parameters of the patient's
tooth.
In one embodiment of the invention, the step of photographing includes the
production of a plurality of photographs representing respective color
characteristics of the original tooth and the color standards selected in
the step of selecting. The photographic images may be in the form of color
print, transparency, or monochrome print.
In accordance with a further method aspect of the invention there is
provided a method of matching the color characteristic of a tooth with a
plurality of color standards, the method comprising the steps of:
1. inspecting visually the tooth and the plurality of the color standards;
2. selecting from the plurality of the color standards a number of the
color standards that are determined in the step of inspecting visually to
approximate the color characteristic of the tooth;
3. photographing the tooth and the number of the color standards selected
in the step of inspecting visually;
4. employing a selectable one of a calorimeter and a spectrophotometer to
measure a color parameter of the images obtained in the step of
photographing of the tooth and of the selected color standards; and
5. determining the one of the selected color standards that is associated
with the photographic image of the selected color standards having the
minimum color difference from the tooth as determined by the measurement
of the step of employing.
In a preferred embodiment of this further method aspect of the invention,
the determination of the color parameters of the dental patient's tooth is
based upon the measured shift in color of a standard in the same
photograph by the photographic process. Again, the shift function of the
standard in the photograph is used with an algorithm to calculate the
original color parameters of the patient's tooth.
In a specific illustrative embodiment of the further method aspect of the
invention, a photograph is produced in the step of photographing is a
color print. As previously noted, the photograph may be any of a color
print, a transparency, or a monochrome print.
In accordance with a system aspect of the invention, there is provided a
system for determining a color characteristic of a tooth. The system is
provided with a plurality of color standards, each for establishing a
predetermined respective color parameter. A photographic apparatus
produces a photographic tooth image of the tooth and respective
photographic color standard images of selected ones of the plurality of
color standards. In some embodiments, the tooth and the color standard
images are imaged in one photograph. An arrangement for measuring a
predetermined color parameter of the photographic tooth image is provided
to produce a tooth image signal responsive thereto and for measuring a
corresponding predetermined color parameter of each of the photographic
color standard images of the selected ones of the plurality of color
standard means, and further to produce respective color standard image
signals corresponding to respectively associated ones of the selected ones
of the plurality of color standard means. There is additionally provided
an arrangement for comparing the tooth image signal to each of the color
standard image signals.
In a specific illustrative embodiment of the system aspect of the
invention, the arrangement for measuring photographic image color
parameters is a colorimeter. In other embodiments, it is a
spectrophotometer. The photographic apparatus includes a camera. The
camera may have, in respective embodiments, a color film, a monochromatic
film; a transparency film, or any other suitable image recording medium
installed therein. Alternatively, the camera may be of the instant
development-type, such as a Polaroid.RTM. camera. A lighting arrangement,
as will be described in detail below, is arranged in certain embodiments
to cooperate with the photographic equipment, and produces a predetermined
light which may have a determined color character, illustratively as a
result of translucent filtering. Also as will be described below, the
plurality of color standards are each provided with an aperture for
facilitating viewing of the tooth therethrough. The arrangement for
comparing the tooth image signal to each of the color standard image
signals includes, in certain embodiments, a numerical display associated
with the arrangement for measuring.
BRIEF DESCRIPTION OF THE DRAWING
Comprehension of the invention is facilitated by reading the following
detailed description in conjunction with the annexed drawings, in which:
FIG. 1 is a diagram that is useful to illustrate the technological
disciplines incorporated in the present invention;
FIG. 2 is a schematic representation of an arrangement for photographing
the tooth of a dental patient and a pair of color standards
simultaneously, and further illustrating schematically arrangements for
measuring color parameters and calculating a photographic shift function;
and
FIG. 3 is a function block diagram that illustrates, in simplified form,
the major steps of the inventive process.
DETAILED DESCRIPTION
FIG. 1 is a diagram that is useful to illustrate the technological
disciplines incorporated in the present invention. As stated hereinabove,
the present invention constitutes a hybrid system of photocolorimetry that
combines visual, photographic, and calorimetric approaches to form a
system of matching the color of teeth.
FIG. 2 is a schematic representation of an arrangement for photographing
the tooth of a dental patient and a pair of color standards
simultaneously. The method of the present invention involves, in a first
aspect thereof, three steps. First, as shown in FIG. 2, a practitioner
(not shown) uses a plurality of color standards and selects therefrom the
two or three closest matches to the patient's teeth, preferably under
color corrected or balanced light sources. FIG. 2 shows first and second
color standards, 10 and 11, respectively, arranged adjacent to a tooth 13
of a dental patient 15. Next, the practitioner photographs with a camera
17 the patient's tooth 13, and the previously selected color standards 10
and 11. These items can be photographed individually. However, it is
preferred that the standards be photographed together with the teeth, as
shown in the specific illustrative embodiment of FIG. 2, since each
photograph will be characterized by a unique color shift. As will be
discussed in greater functional detail below, the output of camera 17,
which will be in the form of a photographic image (not shown) of tooth 13
and standards 10 and 11, is subjected to a color measurement system 18
where a color shift spectrum (not shown) for the process by which the
photographic images were formed is determined, by reference to the known
spectrum of a color standard. The output of the color measurement system
is directed to a calculation system 19 that will calculate the color
spectrum of the tooth, combine same with, in this specific illustrative
embodiment of the invention, information related to a CIE standard source
and CIE color-matching functions for equal energy spectra, to determine
CIE color parameters, as described hereinbelow.
FIG. 3 is a function block diagram that illustrates, in simplified form,
the major steps of the inventive process. Function block 20 sets forth the
observation of the tooth of the dental patient (not shown in this figure),
as described above. The practitioner (not shown) then observes visually at
function block 21 the color standards and makes a preliminary selection of
the ones thereof that appear closest to the color of the patient's tooth.
At function block 22, the practitioner photographs the tooth of the
patient simultaneously with the visually selected color standards, as
described above with respect to FIG. 2.
The practitioner then, at function block 23 of FIG. 3 measures the color
parameters of the photographic images of the teeth and color standards on
the clinical photograph with a colorimeter in the known CIE L*a*b* or
other color system. In a preferred embodiment, the match is determined by
calculating, as set forth in function block 24, the color difference in
accordance with the following relationship:
##EQU1##
wherein the closest color characteristic match between the patient's tooth
and the color standards corresponds to the particular color standard, the
image of which has associated therewith the minimum color value difference
from the tooth image, as determined by the calorimeter.
The present invention is based in part on the discovery by the inventor
herein that although the photographic process shifts the colors of teeth
and of the color standards, relative color differences are preserved among
color samples that are relatively close in color. It has also been found
that subtractive color photography, or additive color photography with
monochrome photography, may be employed in the practice of the invention.
The calorimetric measurements on the photographs, as set forth herein,
serve to substitute for the prior art's problematical final visual
matching by the practitioner to select the closest of the color standards.
In addition to obviating the need for visual matching of the color of teeth
to select the closest color standard, the present invention affords the
additional advantage of providing a method for estimating the numerical
color parameters of the teeth. These parameters are useful in formulating
new materials when the color characteristic of the teeth does not match
existing materials or the color characteristics of the color standards. In
the practice of this additional advantage afforded by the present
invention, the photographing color standards that have been determined
visually to approximate the color characteristic of the teeth, as well as
the teeth, is performed as previously described. However, a
spectrophotometer (e.g., Color Eye, Macbeth, Inc.) is used to determine
the spectral R.sub.o (.lambda.) reflectance of the color standards and the
photographic images of the standards and teeth from around 400 nm to
around 700 nm. These data are used as follows in estimating the color
parameters of the teeth:
First the color shift function of the photographic process is determined by
dividing the spectral reflectance of the photographic image of the closest
matching color standard, R.sub.ps (.lambda.) by the spectral reflectance
of the color standard, R.sub.os (.lambda.) to give the shift function,
S.sub.p (.lambda.),
##EQU2##
This shift function is then used to estimate the color parameter of the
tooth by dividing the spectral reflectance curve of the photographic image
of the tooth by the shift function as follows:
##EQU3##
Once the calculated spectral response curve of the tooth is obtained, the
calculation of CIE or other color parameters for a given standard light
source and observer is routine and is known to persons of skill in the art
of colorimetry.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In order to determine a color match for a patient's teeth using the
photocolorimetric system, a number of photographic processes may be used
in conjunction with visual matching and colorimetry. Photography that
produces a negative from which color prints can be made provides an
excellent photographic process. Instant color photography using Polaroid
technology has the advantage of simplicity and speed in producing a print.
Reversal color films which reproduce color by subtractive three-color
synthesis with three layers may be used in the form of slides. Additive or
trichromatic photography uses black and white panchromatic film with
colored filters and is applicable to this present invention. Teeth are
photographed along with tooth color standards with colored lens filters
(e.g., red, blue, yellow, green, etc.) on black and white panchromatic
film. CIE L* measurements are then made on the photographed tooth and
color standard images with a calorimeter. The best matching color standard
to the teeth will have the closest L* values in photographs made with the
three filters, since this represents the lowest .DELTA.E* value for a
black and white photograph with a* and b* values close to zero.
The control of incident lighting is an essential element in successful
determination of tooth color matches with photocolorimetry. Generally, any
photographic filter that will enhance the saturation of the low chroma
teeth images will increase the accuracy of color measurements. The yellow
and yellow-red colors of teeth and matching shade guides may be enhanced
in photographs by the use of colored photographic filters placed over the
lens of the camera or over the light source. For example, the yellow color
of teeth was enhanced by placing a combination of 5Y and 2.5 magenta
Wratten filters, available from Kodak, Inc., over the flash attachment of
the camera. The filtered light reaching the teeth during photography is
therefore slightly enriched in yellow-red which increases the saturation
of the color of the photographic images. This increase in saturation
results in an increase in the CIE b* values measured, which increases the
ability to detect small color differences between the teeth and the color
standards. In other situations, filters of a complementary color will
better enhance color differences between the color standards and the
teeth. Persons skilled in the field of photography can select appropriate
filters for illumination based on general colors of the teeth to enhance
color differences. In most situations, daylight or conventional Xenon
strobe lights will function satisfactorily in the practice of the
invention. In addition to the spectrum of the light, the intensity of the
incident light must be uniform on the teeth and on the color standards.
Otherwise, color differences between the photographed images of the teeth
and color standards will result from the uneven lighting rather than from
actual differences in surface reflectance spectra.
Uniform distribution of light is achieved in two ways. First, gloss which
represents areas on the objects where there is high specular reflection
from the light source, needs to be minimized. An effective method of
minimizing gloss on areas of the object where color measurements will be
made involves controlling the angle of incidence and the angle
photographed. In this way, the site of the gloss may be directed away from
the center of the tooth or other area where the color measurements of the
photographic image will be made. For example, an incident light arranged
at approximately between 45.degree. and 75.degree. with respect to the
surface and above the mandibular central incisor teeth, with the camera
lens perpendicular to the teeth, will direct the gloss area to the
gingival third of the teeth.
The use of polarizing filters affords another method of reducing gloss.
Still another important approach to obtaining uniform lighting of the
teeth and of the color standards involves keeping the teeth and the color
standards as close together as possible in space to the incident light
source. In the practice of one such method, conventional shade guide color
standards are placed adjacent to the teeth with incisal edge to incisal
edge, rather than proximal surface to proximal surface, with the shade
guide tooth over a natural tooth, as is commonly done. It is noted that
achieving uniform lighting and avoiding gloss in critical areas of the
teeth being photographed are within the capabilities of those having
ordinary photographic skills and conventional equipment.
EXAMPLE 1
A tooth was selected for color matching with the Bioform Shade Guide
(Dentsply International, Inc., York, Pa.). The tooth and Bioform Shade
Guide color standards were illuminated with the Ney-Lite, which provides
CIE Illuminant C (J. M. Ney Co., Hartford, Conn.). Three approximate color
matches were selected visually (#59, #51, and #91) from the Bioform Shade
Guide. Next, the tooth, along with the approximate shade matches, was
photographed with a Nikon single lens reflex camera with Kodak Vericolor
Type III professional film, taking care to avoid specular reflection in
the center of the tooth and shade guide teeth. The film was then sent for
C-41 processing to produce color negatives. Color prints were then made
with RA chemistry and Fuji paper. Color measurements were then made on the
photograph of the tooth and shade guide images in the CIE L*a*b* system
and the color differences calculated between the tooth image parameters
and those of the Bioform standards. The CIE .DELTA.E* values between the
59, 51, and 91 standards and the tooth average were calculated with the
formula:
##EQU4##
The values of .DELTA.E were 1.58, 6.59, and 7.03, respectively. Therefore,
Bioform shade #59 was selected as the closest shade to match for the
tooth.
EXAMPLE 2
A tooth color was matched with three Munsell color standards visually under
daylight. The tooth and the Munsell color standards (5Y 8/12, 5Y 8/6, and
5Y 8/4) were photographed with Kodak T-max 100 black and white film using
a Nikon.RTM. F3 camera. Three photographs were made with green, red, and
blue filters. The CIE L* values were measured of the tooth and Munsell
color standard images on the black and white prints made from the
processed negatives. The L* values found are given below:
______________________________________
L* Values
Subject Green Filter Red Filter
Blue Filter
______________________________________
Tooth 81 86 54
5Y 8/12 76 86 22
5Y 8/6 80 87 54
5Y 8/4 80 86 67
______________________________________
The best match between the L* values of the Munsell color standards and the
tooth color was for the 5Y 8/6 sample, which was chosen as the color match
for the tooth.
EXAMPLE 3
This example illustrates a method of matching a tooth color against a
bioform shade guide B91 standard. The tooth and the B91 standard were
photographed together with Kodak.RTM. Vericolor Type III professional film
with a Nikon.RTM. single lens reflex camera. The film was developed using
C-41 processing, and a color print was obtained using C-41 processing and
Fuji.RTM. paper. The reflectance spectrum of the B91 color standard,
R.sub.o (.lambda.), was measured along with the reflectance spectrum of
the B91 photographic image, R.sub.p (.lambda.), using a Macbeth Color Eye
Spectrophotometer. In accordance with function block 24 of FIG. 3, the
shift function, S.sub.p (.lambda.), of the B91 color standard was
calculated as follows:
##EQU5##
using a computer for .lambda. values between 400 and 700 mm. The
reflectance spectrum for the tooth photographic image, R.sub.p (.lambda.),
was measured with the spectrophotometer. Then, in accordance with function
block 25 of FIG. 3, the original tooth color spectrum, R.sub.o (.lambda.),
was then calculated with the relationship:
##EQU6##
where S.sub.p (.lambda.) is the shift function of the B91 standard. Once
R.sub.o (.lambda.) for the tooth was obtained, the CIE L*a*b* parameters
were calculated using the Macbeth Color Eye spectrophotometer program. The
CIE L*a*b* parameters obtained were 76, -0.42, 14, and 79, -1.0, 16
respectively, for the B91 standard and tooth.
Although the invention has been described in terms of specific embodiments
and applications, persons skilled in the art can, in light of this
teaching, generate additional embodiments without exceeding the scope or
departing from the spirit of the claimed invention. Accordingly, it is to
be understood that the drawing and description in this disclosure are
proffered to facilitate comprehension of the invention, and should not be
construed to limit the scope thereof
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